Rotary joint



July 4, 1950 c. w. KLosTERMANN 2,514,160

v ROTARY JOINT Filed Oct. 21, 1944 2 Sheets-Sheet 1 Filed Oct. 21, 19442 Sheets-Sheec 2 APatented July 4, 1950 UNITED STATE OFFICE ROTARY JOINTCurt W. Klostermann, Chicago, Ill.

Application October 21, 1944, Serial No. 559,820

4 Claims. 1

This invention relates to rotary joints and is more particularlyconcerned with rotary joints employed for connecting the ends of radiofrequency transmission lines of the type embodying conductors held incoaxial relation by means of a solid dielectric.

More particularly, this invention relates to rotary joints adapted foruse with radio installations in which it is desirable to rotate thereceiving or transmitting antenna in order to receive or transmitsignals in various directions. It is now common practice to supply radiofrequency energy through coaxial conductors in which a center conductoris coaxially positioned within an outer conductor or shield. It hasheretofore been common practice to construct coaxial transmission lineshaving a central conductor mechanically and electrically isolated fromand held in coaxial position with the outside conductor or shield bymeans of insulating spacers or discs located at spaced intervals. Inthis type of construction, the dielectric between the center conductorand the shield is largely air and, in order to prevent moist air fromcondensing and causing moisture to form within this space withconsequent deterioration of the electrical characteristics of thetransmission line, it was necessary to ll such lines with dried air orother gas under pressure. Due to the possibility of air leakage from thetransmission line, it was also necessary to provide pressure indicatingmeans.

While rotary joints and connectors have been widely employed for use intransmission lines employing air or gas as a dielectric, such joints andconnectors are similar in construction to the transmission lines in thatthe coaxial conductors are maintained in position by means of insulatingspacers and the dielectric is predominantly air or gas. This type ofjoint and connector, therefore, is objectionable for the same reasonspresented in consideration of the air lled transmission line and, inaddition thereto, considerable diiiiculty is encountered in maintainingthe transmission line and connecting rotary joints tight and free fromleaks, particularly when same are subjected to vibration and shock.

Due to these objectionable features, such transmission lines are nowbeing replaced with cables having coaxial conductors mechanically andelectrically isolated and held in coaxial position by means of solid,semiflexible dielectric such as polyethylene. In the use of the soliddielectric in cable construction, there is no air space between thecenter conducto-r and the outside shield and a better coaxial alignmentmay be maintained.

Other advantages to be derived from the use of a coaxial cable employinga solid dielectric are:

1. Freedom from corona diiiiculties.

2. Much higher voltage breakdown characteristics because oi the use of asolid dielectric in place of air as an insulating medium.

3. Freedom from moisture condensation.

4. Constancy of electrical and mechanical characteristics when installedin locations where vibration and shock are present.

It is an object of the present invention to provide a rotary joint orconnector adapted for use with coaxial transmission lines embodying asolid dielectric, and further contemplates the provision of a device ofthis kind which possesses all the inherent advantages of the cableconstruction in order that the electrical or mechanical properties ofthe transmission line system will not be prejudiced in any way due tothe introduction of the rotatable joint cr connector therein. A rotaryjoint or connector constructed in accordance with the present inventionernbodies the following novel features:

1. Is as free from corona as the cable to which it is attached.

2. Has as high a voltage breakdown characteristic as the cable.

3. Is free from air spaces in which moisture could condense. K

4.. Has continuity of impedance throughout its length.

5. Is capable of trouble-free mechanical and electrical operationthrough many thousands of revolutions.

6. Has constancy of electrical and mechanical characteristics whensubjected to vibration and shock.

This invention embodies other novel features, details of constructionand arrangement of parts which are hereinafter set forth in thespecication and claims and illustrated in the drawings, wherein:

Fig. 1 is a view partly in section and partly in elevation showing arotary joint embodying features of this invention.

Fig. 2 is an end view of same with the cable omitted.

Fig. 3 is a view partly in section and partly in elevation showing amodified form of this invention.

Fig. 4 is an end view of same, partly in section.

Fig. 5 is a detailed view showing a stator ground sleeve.

Referring now to the drawings for a better understanding of thisinvention and more particularly to Figs. 1 and 2 therein, the rotaryjoint connector is shown as comprising a stator shell I I which is boredat I2 to receive a standard type of solid dielectric coaxial cable I3.The

cable I3 is of well known construction and of theV type now commonlyemployed for feeding radio frequency energy to antennas. As shown in thedrawings, the cable comprises an Vinner con-M ductor I4 and an outerconductor I6 which are held in coaxial relation by means of a soliddielectric Il. The outer conductor I is formed of woven wire covered bya vinyl jacket I8.

Prior to coupling engagement of the ends of the cable I3 withintherotary joint or connector, the ends of the cables are pre-formed bystripping the vinyl jacket and braided conductor back from therespective ends of the cable, then forming a tapered shoulder I9 on thesolid dielectric, and counter-boring the center conductors I4 at 2| toreceive male and female contact members 22 and 23, respectively, forsoldered engagement to the conductors I4. The end of the contact member22 is formed with one or more longitudinal slotsv 24 to provide a springcontact engagement with the contact member 23. The contacts 22 and 23are of the same diameter as the conductors I4 to provide a perfectcontinuity of impedance therethrough.

A dielectric sleeve 26 is mounted within the bore I2 of the stator shellII and has its ends formed with frustro-conical recesses 21, one ofwhich receives the tapered shoulder I9 formed on the solid dielectric Ilof the cable. The dielectric sleeve is provided with an annular rib 28for engagement against an annular shoulder 29 formed within the bore I2of the stator shell II. The stator shell is internally threaded at 3| toreceive an externally threaded stator ground sleeve 32 which acts tosecure the annular ring 28 against the shoulder 29. The ground sleeve 32is secured in position on the stator shell by means of a set screw 33.

The stator shell II is formed with a tapered shoulder 34 for engagementunder the braided outer conductor I6 and the vinyl jacket I8. The vinyljacket I8 and the braided outer conductor I6 are engaged against theshoulder 34 of the stator shell II by means of a seal and ground ring 36and a seal and ground nut 31. The seal and ground nut 31 is internallythreaded at 38 for engagement on the threaded end of the stator shell IIand is externally threaded at 39 to receive an internally threaded clampnut 4I. A clamp ring 42 is mounted Within the clamp nut 4I for taperedwedging engagement against a slotted clamping collet 43. Contraction ofthe clamping collet 43 against the outer periphery of the vinyl jacketI3 acts to firmly secure the cable to the stator shell I I. A neoprenesealing ring gasket 44 is mounted on the inner endof the seal and groundring 3Sto seal this portion 0f the joint against the entrance ofmoisture.

A rotor shell 5I is journaled for rotational movement in a bearing 52which is secured to a ange portion 53 of the stator shell II by means ofscrews 54. The rotor shell is bored at 5i) to receive a dielectricsleeve 59 which is formed with an annular ring 6I for locked engagementagainst a shoulder 62 by means of a threaded rotor ground sleeve 63. Therotor ground sleeve 63 is held against displacement by means of a setscrew 64. The inner end of the dielectric sleeve 59 is formed with atapered shoulder 5B for engagement within the tapered recess 21 formedin the dielectric sleeve 25. The other end of the dielectric sleeve 59is formed with a frustreconical recess 57 to receive the taperedshoulder I9 provided on the end of the cable dielectric I'I. The statorground sleeve 32 is slotted at 65 to provide a plurality of resilientfingers 66 which bear against the outer peripheral contact surface 31formed on the rotor ground sleeve 63.

The rotor shell 5I is connected to the other end of the cable I3 in themanner heretofore described in connecting the cable to the stator shellI I, and as similar parts are employed for making the connection, theseparts are indicated by similar members. The means employed for turningthe rotor shell with respect to the stator shell comprises a tube 'IIwhich is connected to the rotor shell 5I by means of a split coupling12. The split coupling is formed in two parts joined together by meansof screws 73. To insure against relative movement between the tube II Yand the rotor shell 5I, key pins 'I4 and 'I6 are employed for keying thecoupling to the rotor shell and tubing, respectively.

The bearing surfaces provided for the rotor shell are lubricated througha threaded opening Il by removing a screw 'I8 therefrom. The lubricatingfluid is retained against leakage from the bearing surfaces by means ofpacking rings 'I9 held in engagement against the outer surface of thestator ground sleeve by means of a packing nut 8| threaded onto theinner end of the rotor shell. Packing rings 82 are employed to engagethe outer surface of the rotor shell and held in position by means of apacking nut 83 which is threaded onto the rotor shell bearing 52. Duringassembly of the rotary joint, the threaded openings provided for thelocking screws 33 and 64 are sealed at their outer ends by a suitablerubber cement such as the type manufactured by the Goodyear Rubber Co.and known as AF 12C rubber cement.

In order to eliminate air spaces within the rotary joint, the ends ofthe cable dielectric I'F and the ends of the dielectric sleeves 26 and59 arecoated prior to assembly with a suitable paste or grease-likesubstance, such as Dow-Corning Sealing Compound No. 4 which insures thatno air will be present when the joint is assembled. Such a sealingcompound must necessarily have good electrical characteristics and mustnot interfere with the electrical contact of the metal parts. Use of thesealing compound upon tapered dielectric junctions of the type shown anddescribed insures that there will be no corona or voltage breakdowndifficulties in the completed assembly, and further that there will beno air Spaces in which moisture can condense.

It will be observed that perfect continuity of impedance is preserved bycontinuing the center conductor at its original diameter through therotary joint and doing likewise with the outer conductor. By preservingthe continuity of the center conductor and outer conductor diameters,

the characteristic impedance of the transmission line through the rotaryjoint will be uniform and the same as that of the cable, providing thedielectric used in the sleeves 26 and 59 has the same dielectricconstant as that of the Cable insulation itself. Actual tests have shownthis type of rotary joint to be free from objectionable reiiectionlosses caused by impedance discontinuities for frequencies up as high as3000 megacycles.

Referring now to lFigs. 3 and 4 in the drawings, a modified form of therotary joint construction is provided by which transmission line cablesmay be attached at right angles to the longitudinal axis of the rotaryjoint. Since it is impossible to bend large cables around a small radiuswithout damaging the dielectric, it is desirable to make the right angleconnection within the joint itself. In this form of the invention arotor shell 86 is journaled within a bearing member 81 secured to astator shell 8S by means of screws 8S. A pair of dielectric sleeves 9iand 92 are secured within the rotor shell B and stator shell 83,respectively, by means of the rotor ground sleeve E3 and stator groundsleeve 32, respectively. The dielectric sleeves are formed withfrustro-conical engaging surfaces at 93 and have their outer endsabutting against dielectric plugs 9i!- and 9K5, respectively, disposedwithin elbow ttings 91 and 98, respectively. Fittings 9'! and S3 are inthreaded engagement with the outer ends of the rotor shell 85 and statorshell 231i, respectively, and are secured against relative movementtherewith by means of set screws S39. Ring gaskets lili, formed ofneoprene or the like, are provided in the threaded connections betweenthe elbow fittings and their respective shells.

The ends of the transmission cable are connected to the outer ends o theelbow fittings 91 and 98 by the method heretofore set forth in thedescription of the preferred form of this invention and by the use ofsimilar parts which have accordingly been assigned similar numbers. Theinner conductors lll are counter-bored to receive contact members il??which are soldered to the outer ends of conductors 183 and lcd,respectively. The inner ends of the conductors W3 and iill are formedfor electrical rotational contact by counter-boring the conductor 1&3 toreceive the spring lingers liliof the conductor i524.

In this form or" the invention, a coupling sleeve lill' is threaded ontothe seal and ground nut 3l in place of the clamping nut All. The tubing'il is inserted within the coupling sleeve lill and held againstdisplacement therefrom by means of set screws M38. Packing materiallili) is employed to prevent leakage between the tubing 'il and thecoupling sleeve, and is held in position by means of a packing nut lllwhich is threaded onto the end oi the coupling sleeve. This form of theinvention is otherwise similar to the construction shown in Figs. l and2.

Another form of a rotary joint may consist of a straight connectionbetween the cable i3 and the stator shell l i as illustrated in Fig. 1,and a right angle connection. for the cable connection with the rotorshell BS as illustrated in Fig. 3.

While this invention has ybeen shown in but two forms, it is obvious tothose skilled in the art that it is not so limited, but is susceptibleci various changes and modifications without departing from the spiritand scope of the claimed invention.

I claim as my invention:

l. In a rotary joint for use with a radio frequency transmission linecable having coaxial conductors held in spaced relation by a soliddielectric, a stator shell for detachable mechanical and electricalengagement with one end of the transmission line cable, a rotor shellfor detachable mechanical and electrical engagement with another end ofthe transmission line cable and rotatably adjustable with respect tosaid stator shell, a pair of dielectric sleeves mounted within saidstator and rotor sleeves and having coaxial inner and outer diameters tocorrespond to the diameters of the solid dielectric of the transmissionline cable, a rotor ground sleeve for securing one dielectric sleeve tothe rotor shell, a sta-tor ground sleeve for securing the otherdielectric sleeve to said stator shell, said stator ground sleeve eingin electrical contact with said rotor ground sleeve.

2. In a rotary joint for use with a radio frequency transmission linecable having coaxial conductors held in spaced relation by a soliddielectric, a stator shell for detachable mechanical and electricalengagement with one end of the transmission line cable, a rotor shellfor detachable mechanical and electrical engagement with another end ofthe transmission line cable and rotatably adjustable with respect tosaid stator shell, a pair of dielectric sleeves mounted within saidstator and rotor sleeves and having coaxial inner and outer diameters tocorrespond to the diameters of the solid dielectric of the transmissionline cable, a rotor ground sleeve for securing one dielectric sleeve tothe rotor shell, a stator ground sleeve for securing the otherdielectric sleeve to said stator shell, said stator ground sleeve beingin electrical contact with said rotor ground sleeve, and a bearingsleeve provided on the stator shell to receive said rotor shell.

3. In a rotary joint for use with a radio frequency transmission linecable having coaxial conductors held in spaced relation by a soliddielectric, a stator shell for detachable mechanical and electricalengagement with one end of the transmission line cable, a rotor shellfor detachable mechanical and electrical engagement with another end ofthe transmission line cable and rotatably adjustable with respect tosaid stator shell, a pair of dielectric sleeves mounted within saidstator and rotor sleeves and having coaxial inner and outer diameters tocorrespond to the diameters of the solid dielectric of the transmissionline cable, a rotor ground sleeve for securing one dielectric sleeve tothe rotor shell, a stator ground sleeve for securing the otherdielectric sleeve to said stator shell, said stator ground sleeve beingin electrical contact with said rotor ground sleeve, said rotor andstator ground sleeves having inner diameters corresponding to thediameter of the outer conductor of the cable and the outer diameters ofthe dielectric sleeves.

4. In a rotary joint for use with a radio frequency transmission linecable having coaxial conductors held in spaced relation by a soliddielectric, a stator shell for detachable mechanical and electricalengagement with one end of the transmission line cable, a rotor shellfor detachable mechanical and electrical engagement with another end ofthe transmission. line cable and rotatably adjustable with respect tosaid stator shell, a pair of dielectric sleeves mounted within saidstator and rotor sleeves and having coaxial inner and outer diameters tocorrespond to the diameters of the solid dielectric of the transmissionline cable, a rotor ground sleeve for securing one dielectric Sleeve tothe rotor shell, a stator 7 ground sleeve for securing the otherdielectric sleeve to vs ajlnstator shell, said stator ground sleeve;beingelectrical Contact with said rotor ground, sleeve, a bearing sleeveprovided on the stator shell to receive said rotor shell, a packingchamber provided between the inner end of the rotor shell and saidstator ground sleeve, and a packing chamber provided between the outerend of said sleeve bearing and said rotor shell.

CURT W. KLOSTERMANN.

REFERENCES CITED The following references are of record in the le ofthis patent:

Number Number 8 UNITED STATES PATENTS Name Date Oakes May 26, 1914Morrison Aug. 9, 1932 Walter Mar. 31, 1936 Bruno July 28, 1942 ReppertOct. 26, 1943 Fraser Mar. 5, 1946 Hallstrand June 24, 1947 Bard July,'29, 1947 FOREIGN PATENTS Country Date Germany Sept. 22, 1891 GermanyDec. 29, 1939

